Generally, various ships such as a bulk carrier, a container ship, a passenger ship, or the like, have employed a fuel supply system using heavy oil (HFO or MDO) for example, bunker C oil, which is a liquid fuel, as propulsion fuel.
In the existing fuel supply system, if heavy oil, or the like, used as fuel combusts, the results from the combustion causes serious environmental pollution due to various harmful substances included in the exhaust gas. Since a demand for preventing environmental pollution is increasingly regulated throughout the whole world, regulations for a propulsion apparatus using heavy oil as fuel oil have correspondingly been reinforced. As a result, costs have been increasingly increased in order to meet these regulations.
In addition, when oil prices have considerably increased due to factors such as depletion of fossil fuel, localized unrest, or the like, several operational problems such as the rapid increase of fuel expenses of a ship using heavy oil as fuel, etc., are caused.
Therefore, research into a fuel supply system, etc., using clean fuel such as LNG (or, LPG, CNG, DME, etc.), that is a liquefied or gaseous fuel without using heavy oil (or, MDO) or using the minimum amount of heavy oil as fuel oil for various ships, but mainly using LNG (or, LPG, CNG, DME, etc.) as fuel when heavy oil (or MDO) becomes expensive or standards required for environmental protection are increased, and only use heavy oil (or, MDO) when heavy oil (or MDO) is cheap or environmental standards are less restricted has been continuously conducted.